Electric power steering systems are known as an example of vehicular systems, i.e. in-vehicle systems. Such an electric power steering system is configured to assist a driver's turning effort of a steering wheel. For example, Japanese Patent Application Publication 2015-161584, referred to as a published patent document, discloses a typical one of these known electric power steering systems.
Specifically, the published patent document discloses an electric power steering system including a motor that generates torque for assisting a driver's turning effort of a steering wheel. The electric power steering system also includes a rotation detector for detecting the rotational angle of the motor. In particular, the rotation detector continuously operates based on electrical power supplied from a battery to perform a predetermined function even if an ignition power supply is off, i.e. an ignition switch is off.